A conventional plate making comprises the steps of imagewise exposing a planographic printing plate material (e.g., a PS plate) through originals and developing the exposed material with an alkali developer to form an image on the planographic printing plate material. However, an undesired image, so-called stripping trace, may be formed at the portions of the thus obtained printing plate where the originals are pasted up. In order to remove such an undesired image, a correction solution or an eraser solution is used.
Recently, as a computer spreads, a CTP (computer to plate) system has been developed in printing fields. In the CTP system, stripping traces do not occur on the surface of printing plates, however, when physical scraping is applied to the printing plate surface, it results in stain, which requires a correction solution or an eraser solution for correction.
A conventional correction process comprises the steps of dissolving undesired image portions or stains on a printing plate surface to remove them from the surface or covering them with a hydrophilic layer. The former process is generally used in a printing plate having a metal support, however, in a hydrophilic support (for example, a hydrophilic support in which a hydrophilic layer is provided on a paper sheet or a polyester film sheet), the hydrophilic layer may be dissolved in the correction solution to reveal the surface of the sheets.
As a countermeasure thereof, a process of covering undesired portions with a correction solution containing inorganic particles and a solvent with a hydrophilic layer is proposed (see for example, Japanese Patent O.P.I. Publication No. 2001-329191). This technique can erase the undesired image portions to be corrected but as printing proceeds employing the printing plate, an image appears on the portions resulting in stain occurrence. A process of covering undesired image portions with a correction solution containing a silane coupling agent is disclosed (see for example, Japanese Patent O.P.I. Publication No. 2003-118261). This technique can increase strength of the hydrophilic layer in which the resin is cross-linked by the silane coupling agent. However, when an image to be corrected is relatively large, the hydrophilic layer is likely to be peeled off to reveal the image under the hydrophilic layer.